The production of polyethylene and copolymers of polyethylene with .alpha.-olefins by Ziegler-Natta polymerization processes has evolved considerably since their introduction in the early 1950s. Control of molecular weight (MW) is important as it influences the final physical properties of the polymer. The MW is controlled by chain transfer reactions which terminate the growth of the polymer chains. A number of such chain transfer processes, including .beta.-H elimination, .beta.-alkyl elimination, and chain transfer to MR.sub.2 (M=Zn, Al, etc.), monomer and hydrogen have been identified. Of these, hydrogen has been found to be the only practical chain transfer agent since it is generally easy to use and normally does not affect the activity of the catalyst. However, there are many cases where even hydrogen does not provide the optimum results due to some undesired side effects (e.g., unresponsive M--R bonds, over activation of the catalyst, too rapid hydrogenation of other functional groups). Therefore, alternative chain transfer agents for use in the production of polyethylene, and copolymers thereof, are highly desirable.
Furthermore, the use of hydrogen as a chain transfer agent results in a non-functional, saturated polymer chain end, whereas terminally functionalized polymer is of great current interest. Such a polymer could be used as precursor for making block or graft polymer and would be expected to exhibit modified chemical and physical properties. A silyl-functional polyethylene of this type has been prepared by Brookhart et al. (Polymer Preprints, Vol. 35(1), 1994) using a cationic cobalt alkyl complex. However, this synthesis presents the following disadvantages: 1) this process is not truly catalytic, 2) the silane does not act as a chain transfer agent and therefore does not control molecular weight of the target polymer; 3) the silane does not regenerate a catalyst; and 4) the method is only effective with ethylene while substituted olefins, such as propylene and butylene, do not react when using the cobalt initiator.
It has also been disclosed by Watson et al. in U.S. Pat. No. 4,965,386 that an olefin can be hydrosilated by contacting the .alpha.-olefin with a silane in the presence of a metallocene catalyst. In this preparation, only the silylated monomeric product was obtained. Watson et al. do not suggest the formation of a polymer or any hydrosilated product derived from repetitive olefin insertion, nor do they suggest the use of ethylene or mixtures of ethylene and an .alpha.-olefin.